Hydrogen (H2) is an attractive energy carrier, with a combustion product that is primarily if not entirely water, and possesses high gravimetric energy density. However, it suffers from an extremely low volumetric energy density. Storing hydrogen under high pressures or in the liquid state can increase volumetric density, but storing hydrogen at high pressures or as a liquid requires expensive, specialized tanks that are expensive, inconvenient, and otherwise disadvantageous, especially in mobile applications. A need exists for materials that simultaneously possess stability, reversibility, and high usable hydrogen density.